1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, a process cartridge and an electrophotographic apparatus. More particularly, it relates to an electrophotographic photosensitive member having a support and provided thereon a photosensitive layer, which photosensitive layer contains a specific high-molecular weight charge-transporting material; and a process cartridge and an electrophotographic apparatus which have such an electrophotographic photosensitive member.
2. Related Background Art
Electrophotographic techniques are in wide use and application in the field of copying machines and also printers because of their advantages that images can be formed in real time and high-quality images can be obtained.
Electrophotographic photosensitive members may be given as one of typical image-holding members used in electrophotographic apparatus. Photoconductive materials used in the electrophotographic photosensitive members include inorganic photoconductive materials such as selenium, cadmium sulfide and zinc oxide. In recent years, however, organic photoconductive materials are on energetic research and development because of their advantages that, e.g., they are free from environmental pollution, promise high productivity and have readiness and future for material designing.
As a matter of course, the electrophotographic photosensitive members are required to have various properties such as electrical, mechanical and also optical properties according to electrophotographic processes to be applied. In particular, electrical and mechanical force such as charging, exposure, development, transfer and cleaning are directly or indirectly repeatedly applied to electrophotographic photosensitive members being used repeatedly. Hence, they are required to have durabilities to these.
In organic electrophotographic photosensitive members making use of organic photoconductive materials, it is usual for the organic photoconductive materials to be dissolved or dispersed in binder resins and used in the form of coating films. To form the coating films, organic photoconductive materials and binder resins are dissolved or dispersed in solvents, followed by coating and then drying.
As the binder resins, materials such as vinyl polymers such as polymethyl methacrylate, polystyrene and polyvinyl chloride, as well as polycarbonate, polyester, polyarylate, polysulfone, phenoxy resins, epoxy resins, silicone resins and copolymers of these are used.
The organic electrophotographic photosensitive members have many advantages that they have superior mass productivity and, in respect of cost, can be manufactured at a relatively low cost. It, however, is not the case that they have satisfied all requirements that are called for as electrophotographic photosensitive members.
With regard to functionality and performance as electrophotography, electrophotographic photosensitive members superior to inorganic electrophotographic photosensitive members have come to be manufactured. However, it is desired to make further improvement in respect of other performance, in particular, what concerns the durability (running performance) in the organic electrophotographic photosensitive members.
As one method of improving the running performance of organic electrophotographic photosensitive members, it is proposed to use various binder resins having superior mechanical strength. However, even though binder resins themselves have superior mechanical strength, they are used in the state a low-molecular weight charge-transporting material is mixed, and hence, the film strength inherent in the binder resins can not sufficiently be brought out. Thus, satisfactory durability (running performance) has not necessarily been achieved in respect of resistance to wear and resistance to scratching.
To make the most of the film strength inherent in the binder resins, the charge-transporting material to be added may be used in a smaller quantity. In such a case, however, a problem may arise such that electrophotographic sensitivity lowers or residual potential rises. Thus, it has not come to achievement of both the film strength and the electrophotographic performance.
For the purpose of preventing film strength from lowering due to the addition of such a low-molecular weight charge-transporting material, the use of high-molecular weight charge-transporting materials is proposed as disclosed in Japanese Patent Applications Laid-open No. 64-9964, No. 2-282263, No. 3-221522, No. 8-208820 and so forth.
However, a great deal of these are not necessarily those having sufficient resistance to wear. Even where they have film strength to a certain extent, there have been disadvantages such that they require too high production cost to be suited for practical use.
From the viewpoint of the resistance to wear of electrophotographic photosensitive members and the cost for their production, these high-molecular weight charge-transporting materials may be used in combination with insulating resins. In such a case, binder resins and high-molecular weight charge-transporting materials may have poor compatibility with each other to make it impossible to produce electrophotographic photosensitive members which can provide good image quality, or to make poor the resistance to wear.
As a high-molecular weight charge-transporting material of a different type, a high-molecular weight charge-transporting material having a repeating structural unit of triphenylamine is proposed (International Publication No. WO99/32537). The high-molecular weight charge-transporting material having this structure has so good compatibility with insulating resins that it has high mechanical strength and high mobility.
Improvement in running performance of an electrophotographic photosensitive member makes it also necessary to provide properties which are stable even in using the electrophotographic photosensitive member repeatedly over a long period of time, where, as a charge-transporting material, it is required to have properties that can not easily cause deterioration, in particular, oxidation deterioration caused by ozone, active oxygen or the like when the electrophotographic photosensitive member is charged electrostatically.
However, while the high-molecular weight charge-transporting material disclosed in the above publication (WO99/32537) has high mechanical strength, it has tended to cause the oxidation deterioration to make properties vary in repeated use in some cases.